1. Field of Invention
The invention relates to magnetic cards.
2. Description of Prior Art
The invention relates more particularly to magnetic cards in the form of credit cards, automatic teller machine cards, membership cards guest cards, pre-paid cards for telephones and the like. Such cards are generally formed of plastic and carry a one or more magnetic tracks which carry binary codes. The codes are normally for identifying the issuer or system and the user as well as a pin number or user signature. It is normal also to provide information about the expiry date, the credit limit or credit currently available for the user and so on. The card often carries a cipher which is a compilation of the system code and the pin number. Generally, the cards are used automatically and card readers provided a points-of-need which are capable of reading the binary codes and controlling an entry terminal to dispense cash or simply identify that the card is genuine and in force, at a point-of-sale for example.
Generally stated, problems arise because such cards are relatively simple to copy or to re-produce and so represent a risk for both issuers and users. Methods of "protection" have therefore been developed already to reduce these problems but most current methods concentrate on making the card itself more difficult to duplicate. Such protection methods include adding a hologram, using especially fine printing, ultraviolet ink, photographs and incorporating active integrated circuit chips (sometimes called "smart" cards). The main disadvantages of these solutions is that they inherently add to the cost of producing genuine cards and in some cases also require generally more sophisticated card readers in use for satisfactory checking of the cards.